This invention relates to apparatus for fusing together electric conductors, and more particularly to apparatus for fusing coil leads to tangs or slots of electric motor armature commutators.
Electric motor parts such as armatures have coils of wire and heavier metal parts (e.g., commutators) to which leads from the coils must be electrically and mechanically connected. A technique which is frequently used for making these mechanical and electrical connections is known as fusing. This technique involves the application of heat and pressure from a fusing electrode to the two elements to be joined (e.g., the commutator and the coil lead) in such a way that these two elements are pressed into firm and intimate contact with one another, and at least one element (e.g., the commutator) is permanently deformed to hold the two elements together. For example, a coil lead wrapped around a commutator tang may be fused to the commutator by deforming the tang down into intimate contact with the lead. Alternatively, a coil lead in a commutator slot may be fused to the commutator by partly crushing the slot in order to close it around the lead. The heat required for the fusing process is typically generated by passing an electric current through the fusing electrode and the elements to be fused and into a ground electrode which contacts another part of the workpiece. The fusing electrode (typically made of tungsten) is the highest resistance element in this circuit and is therefore the element which is heated by this current. Heat flows from the electrode into the elements being fused.
The tip of the fusing electrode which contacts the elements being fused is subject to considerable mechanical, thermal, and even electrical stress. Accordingly, these tips wear quite rapidly and must be changed fairly frequently. European patent application 201,112 shows fusing apparatus in which several fusing electrodes are mounted on a turret which both reciprocates (to perform fusing operations) and rotates (to bring a new fusing electrode into operative position when the preceding electrode is worn). When all the electrodes on a turret are worn, the turret can be removed and either replaced with a new turret or the old turret put back on with the electrodes either replaced or resharpened.
The machine shown in the above-mentioned European application has fairly simple control of the fusing cycle. More recent developments in this technology provide more sophisticated fusing cycle control such as closed loop control based on the displacement of the fusing electrode and/or the force applied by the electrode. Such more sophisticated control is shown, for example, in commonly assigned U.S. Pat. No. 5,063,279, and hereby incorporated by reference herein. While it would be desirable to apply these more sophisticated control techniques to fusing machines having rotating turrets for electrode replacement, there are several respects in which the known rotating turret machines are not especially well suited to such control. For example, the heavier the moving elements are, the more difficult it is to achieve accurate and precise closed loop force and/or displacement control. The more massive the controlled elements, the more serious a problem vibration and inertia become. The known rotating turret fusing machines have relatively heavy moving parts and are therefore not ideally suited to more sophisticated control.
As another example of the respects in which known rotating turret fusing machines do not lend themselves particularly well to more sophisticated control, the known machines typically have only a single rest position of the moving elements. This is the position from which each fusing cycle starts, as well as the position in which the turret is rotated or removed. Accordingly, this rest position must be fairly far from the armature or other workpiece being fused so that the turret can be rotated or removed without risk of damage to the armature. If the machine is intended for fusing armatures of different diameters, the largest armature diameter determines the acceptable rest position. Accordingly, the rest position may have to be quite far from the fusing position for many or even all of the armatures to be fused. This lengthens the fusing cycle stroke, wastes time, and reduces the production rate of the machine. These disadvantages may be especially significant when employing closed loop force and/or displacement control because with such control the fusing head may have to move more slowly in order to allow time for analysis and use of the feedback signal. Accordingly, the shortest possible fusing cycle stroke is generally preferable with closed loop control. Closed loop control may also benefit from having fusing cycle strokes of uniform length regardless of the size of the workpieces being fused. This may reduce or substantially eliminate the cycle control reprogramming that would otherwise be required when adapting the machine to fuse workpieces of different sizes.
In view of the foregoing, it is an object of this invention to provide improved machines for fusing electric motor parts.
It is a more particular object of this invention to provide fusing machines, especially (but not necessarily) of the type having a rotating turret holding several fusing electrodes, which are better adapted to more sophisticated control such as closed loop force and/or displacement control.
It is another more particular object of this invention to provide fusing machines having a fusing stroke of constant length regardless of such factors as deviations or changes in the dimensions of the parts being fused.
It is yet another more particular object of this invention to provide fusing machines with less massive moving parts and which lend themselves to the use of shorter fusing cycle strokes.